Well, if the rumour is true that Gearbox is working on Halo 4 (and people may want to be wary, given the reaction that BiA:HH is getting), most likely they're making it with the next Xbox in mind. I think at that point, consoles will be ready to make the jump to DX10.
Sony's dev cycle is kind of screwed up to the point where the PS3 will probably be competing with the next Xbox for at least 2 or 3 years.
As for trying to mimic the Wii, both companies are trying to do that already - hence the "New Xbox Experience" and SIXAXIS. But I doubt they'll try to compete in the same casual space by trying to have extremely low cost and relatively less powerful hardware.
One thing is that games on Wii simply do not sell as much as games on 360 or PS3. Of course, what people like to bring up is that in the 50-11 NPDs, Wii software is fairly pervasive, I honestly doubt that compares to the number of copies of GTA4 sold. That's the thing with trying to hit that casual mass market. With the "enthusiast", you have people who want to play games as they come out in the same way that people go to watch movies every weekend during the summer. Not so much with casual owners of the Wii. And even then, while Nintendo software sells, their own studies show that most people only play their games for a short time. For example, they found that nearly half of all Wii Fit owners abandon the game after the first week.
I dunno, I guess it depends on how these companies want to make games and their future strategies. Now that Nintendo has the cash, they may try to do something that broadens the casual market yet is also high end. Microsoft could go the other way... and Sony might be trying to push the next high definition format (Rainbow-Ray, it has lasers in every colour!).
